Staphylococcus aureus is a major human pathogen, associated with many types of infection including severe pneumonia. S. aureus activate multiple, often redundant proinflammatory signaling cascades in the lungs involving the airway epithelium as well as neutrophils, alveolar macrophages, dendritic cells and recruited T cells. While neutrophils are critical in the eradication of S. aureus, excessive proinflammatory signaling contributes to pulmonary damage. Our ongoing studies suggest that S. aureus directly activate na?ve CD4+ T cells through expression of multiple superantigens resulting in a hyperinflammatory response. Resident alveolar macrophages, through expression of cytokines such as IL-27 and co-inhibitory signals such as PD-L1, normally function to regulate T cell activation. In the experiments proposed we will establish how S. aureus induced necroptosis may limit the contribution of macrophage immunoregulatory molecules in T cell regulation and whether the macrophage-T cell interaction could be therapeutic target to improve the outcome of methicillin-resistant S. aureus (MRSA) pneumonia. This will be accomplished using wild type and knockout murine models of acute pneumonia, human PBMCs, alveolar macrophages and cell lines. Strategies to prevent T cell activation, by increasing macrophage numbers, blocking co-stimulatory proteins, or delivering exogenous co-inhibitory molecules will be evaluated for their efficacy in the setting of acute MRSA pneumonia. Given the limited efficacy of currently available antibiotics in the setting of MRSA infection, we postulate that enhancing normal immune clearance mechanisms could greatly benefit outcome.